The term "polyphenylene ether resin" includes a family of polymers well known to those skilled in the art, they are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derviatives thereof. By way of illustration, certain of the following polyphenylene ethers are discussed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. Also, the Bennett and Cooper patents, U.S. Pat. Nos. 3,639,656, 3,642,699 and 3,661,848 describe processes for the preparation of polyphenylene ethers. In the Hay patents, the polyphenylene ethers are prepared by a oxidative coupling reaction comprising passing an oxygen-containing gas through a reacton solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes using metal-amine catalysts are found in Bussink et al, U.S. Pat. No. 3,337,499; Blanchard et al, U.S. Pat. No. 3,219,626; Laakso et al, U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,166; Hori et al, U.S. Pat. No. 3,384,619; Faurote et al, U.S. Pat. No. 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are well known from patents such as Wieden et al, U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al, U.S. Pat. No. 3,573,257 (metal-alcoholate or phenolate); Kobayashi et al, U.S. Pat. No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as a peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to noncatalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al, U.S. Pat. No. 3,382,212. All of the patents which are mentioned above are incorporated herein by reference.
The Cizek patent, U.S. Pat. No. 3,383,435 discloses compositions of polyphenylene ether resins and styrene resins. The thermoplastic composition disclosed by Cizek may include a rubber-modified styrene resin, as well as crystal polystyrene. In general, the particularly disclosed crystal polystyrene resins are of a relatively high molecular weight. The disclosure of the Cizek patent is hereby incorporated by reference.
It is now been found that when a thermoplastic molding composition is prepared from a polyphenylene ether resin and a rubber-modified, high impact styrene resin, it is possible to reduce the melt viscosity by adding a minor proportion of a homopolystyrene that has a number average molecular weight between 30,000 and 60,000.
The resulting product which is obtained according to this invention has an improved surface appearance in that the gloss is improved and the surface is substantially completely free of defects. Also, the addition of the lower molecular weight homopolystyrene while reducing the melt viscosity does not appreciably reduce the heat deflection temperature.
It is, therefore, a primary object of this invention to provide improved thermoplastic molding compositions which include polyphenylene ether resins and rubber-modified, high impact styrene resins.
Another object of this invention is to provide theromplastic molding compositions which have a reduced melt viscosity which facilitates the fabrication of molded articles having complex configurations and permits the use of a faster molding cycle.
Still another object of this invention is to provide thermoplastic molding compositions having an improved surface appearance. These and other objects of this invention will be readily apparent from a reading of the description of the invention.